As the recent technique used in the process for producing semiconductor devices, wiring forming technique using Damascene method is known. In this method, a barrier metal layer comprising a hard metal or the like is formed on an insulating layer which is obtained by forming a depression for wiring such as a hole or a trench in an insulating film provided on a process wafer, then a wiring material such as tungsten, aluminum or copper is accumulated in the depression for wiring to form a wiring material layer, and thereafter the wiring material layer and barrier metal layer which have been formed on a region other than the depression for wiring are removed by chemical mechanical polishing to expose the surface of the insulating layer in said region and to leave the barrier metal and the wiring material in only the depression for wiring, whereby wiring called Damascene wiring is formed.
In the process for forming the Damascene wiring, there are the following problems attributable to the chemical mechanical polishing. Because relatively soft metals which are preferably used as wiring materials, such as copper, are polished easily, the wiring material layer is excessively polished especially when a width of wiring to be formed is large. Therefore, formation of a concave portion, i.e., so-called dishing, is caused at the center of the resulting wiring, and a flat polished surface cannot be obtained in some cases. Moreover, occurrence of scratches may cause disconnection of wiring.
Further, it is not easy to efficiently polish the barrier metal layer comprising a metal of high hardness such as tantalum.
Furthermore, in the case where a porous substance having a small dielectric constant is used for an insulating film to constitute an insulating layer, if a chemical mechanical aqueous dispersion having low pH is used as a processing liquid for the chemical mechanical polishing, a satisfactory polishing rate is not obtained. On the other hand, if a chemical mechanical aqueous dispersion having high pH is used, the insulating layer is sometimes polished excessively. Moreover, even if any of these chemical mechanical polishing aqueous dispersions is used, it is not easy to inhibit occurrence of scratches.
Accordingly, as a chemical mechanical polishing method for forming Damascene wiring, a method of performing multi-step chemical mechanical polishing on a polishing-intended surface is usually used. In general, there has been widely adopted a two-step polishing method wherein two-step polishing consisting of a first polishing step to mainly polish a wiring material layer comprising a wiring material such as copper and a second polishing step to mainly polish a barrier metal layer is performed.
As the two-step polishing method, there has been proposed, for example, a method wherein in the first polishing step a removal-intended wiring material layer portion of the copper layer that is a wiring material layer is completely removed and in the second polishing step a removal-intended barrier metal layer portion is completely removed (this method being also referred to as a “first method” hereinafter). In this first method, however, there is a problem that it is difficult to correct, in the second polishing step, dishing that has been not a little caused in the first polishing step, and hence favorable Damascene wiring cannot be formed.
Further, there has been proposed a method wherein in the first polishing step a removal-intended wiring material layer portion of the wiring material layer is removed except a part of said portion so that dishing should not be caused and in the second polishing step, while the remainder of the removal-intended wiring material layer portion is completely removed, a removal-intended barrier metal layer portion is completely removed (this method being also referred to as a “second method” hereinafter).
As processing liquids employable in the above-described two-step polishing methods, various chemical mechanical polishing aqueous dispersions have been proposed.
The chemical mechanical polishing aqueous dispersion for use in the second polishing step of the second method needs to have not only a function of removing copper that is a wiring material and a barrier metal at the same time by the chemical mechanical polishing but also a function of polishing a surface of an insulating layer. Therefore, there has been proposed a chemical mechanical polishing aqueous dispersion having polishing properties that when each of a copper film, a barrier metal film and an insulating film is chemically mechanically polished under the same conditions using said dispersion, both removal rate ratios (RBM/RCu) and (RIn/RCu) approximate to 1, wherein the RBM/RCu is ratio of a barrier metal film removal rate (RBM) to a copper film removal rate (RCu) and the RIn/RCu is ratio of an insulating film removal rate (RIn) to a copper film removal rate (RCu) (see, for example, Japanese Patent Laid-Open Publication No. 196336/2001).
In the Japanese Patent Laid-Open Publication No. 196336/2001, a chemical mechanical polishing aqueous dispersion containing an abrasive, an oxidizing agent and a specific removal rate-adjusting agent is disclosed, and in the working examples, a chemical mechanical polishing aqueous dispersion containing a polishing rate-adjusting agent consisting of potassium maleate and having a removal rate ratio (RBM/RCu) of 0.66 to 1.11 and a removal rate ratio (RIn/RCu) of 0.72 to 1.42 is prepared, and two-step polishing using this chemical mechanical polishing aqueous dispersion in the second polishing step is carried out.
In recent years, however, polishing performance of a chemical mechanical polishing aqueous dispersion used in the first polishing step of the second method has been relatively enhanced, and consequently, the wiring material layer portion remaining after the first polishing step tends to become smaller than before. In the second polishing step, therefore, it is necessary to increase the proportion of the polished amount of the barrier metal layer as compared with the wiring material layer and the insulating layer. However, the chemical mechanical polishing aqueous dispersion described in the Japanese Patent Laid-Open Publication No. 196336/2001 has a removal rate ratio (RBM/RCu) of approximate 1, so that copper that is a wiring material is sometimes polished excessively, and a highly precisely flat polished surface cannot be obtained occasionally.
Accordingly, as a chemical mechanical polishing aqueous dispersion for use in the second polishing step, a chemical mechanical polishing aqueous dispersion having polishing properties suitable for the above circumstances, that is, polishing properties that the removal rate ratio (RBM/RCu) is moderately large and the removal rate ratio (RIn/RCu) approximates to 1 is desired.
In Japanese Patent Laid-Open Publication No. 151451/2002, an aqueous dispersion having a removal rate ratio (RBM/RCu) of 0.5 to 200 is disclosed as a chemical mechanical polishing aqueous dispersion used in the second polishing step of the two-step polishing method. The polishing rate ratio (RBM/RCu) of this aqueous dispersion is adjusted by using benzotriazole as a polishing rate-adjusting agent and controlling its concentration. In this case, however, the removal rate ratio (RIn/RCu) also varies largely, so that if the removal rate ratio (RIn/RCu) is set in the vicinity of 1, the removal rate ratio (RBM/RCu) is markedly increased, and if the removal rate ratio (RBM/RCu) is relatively decreased, the removal rate ratio (RIn/RCu) is markedly decreased.
Thus, a chemical mechanical polishing aqueous dispersion having the polishing properties that the removal rate ratio (RBM/RCu) is moderately large and the removal rate ratio (RIn/RCu) approximates to 1 has not been proposed yet.
Recently, also in the first method, polishing performance of the chemical mechanical polishing aqueous dispersion for use in the first polishing step has been enhanced and inhibition of occurrence of dishing has become possible, so that the first method has been reconsidered as a method for forming Damascene wiring. Also as the chemical mechanical polishing aqueous dispersion for use in the second polishing step of the first method, an aqueous dispersion having polishing properties that the barrier metal layer removal rate is relatively large as described above has been desired.
In Japanese Patent Laid-Open Publication No. 110597/2002, a chemical mechanical aqueous dispersion containing, as removal rate-adjusting agents, quinolinecarboxylic acid and another organic acid in combination is disclosed, and in the working examples, a chemical mechanical polishing aqueous dispersion containing oxalic acid or malonic acid as another organic acid and having a mass ratio (WB/WC) of the content (WB) of quinolinecarboxylic acid to the content (WC) of another organic acid being 1.25 to 5 is specifically disclosed. The invention of the Japanese Patent Laid-Open Publication No. 110597/2002, however, is intended to enhance the removal rate of the wiring material, particularly copper, and this publication neither describes a removal rate ratio (RBM/RCu) and a removal rate ratio (RIn/RCu) nor suggests two-step polishing.